Apparatus for removing unburned carbon in fly ash

ABSTRACT

Unburned carbon is efficiently separated according to the properties of fly ash. An apparatus is provided which comprises: a slurry preparation tank ( 10 ) in which water (c) is added to fly ash (a) to produce a slurry (d); a scavenger addition device ( 20 ) for adding a scavenger (e) to the slurry (d); a vertical surface-modification device ( 30 ) in which the slurry after addition of the scavenger is stirred at a high speed to impart shear force thereto and thereby cause the scavenger (e) to adhere to the surface of unburned carbon (b) contained in the slurry; a regulating tank ( 60 ) in which a blowing agent (f) is added to the slurry (d′) which has undergone surface modification with the surface modification device; and a flotation machine ( 70 ) with which the unburned carbon (b) is floated together with bubbles (n) and separated from the slurry containing the blowing agent.

FIELD OF THE INVENTION

This invention pertains to an apparatus for removing unburned carbonfrom fly ash and in further detail to an apparatus for removing unburnedcarbon from fly ash that effectively removes the unburned carbon fromfly ash generated in a coal fired power plant or a fluid bed combustionfurnace.

DESCRIPTION OF THE RELATED ART

Fly ash (FA) generated in coal fired power plants and fluidized bedcombustion furnaces is used as a raw material for cement and asartificial, lightweight aggregate or as a cement admixture.

However, when using fly ash as a cement admixture, as any unburnedcarbon included in the fly ash absorbs AE agents and water reducingagents, it is necessary beforehand to supply excess AE agents and waterreducing agents in excess to allow for the absorbed amount and thus isuneconomical. Furthermore, because unburned carbon is water repellent, anegative effect is produced because it separates from the concrete whenit is cast and rises to the surface creating black areas due to theunburned carbon in the concrete-jointed portion. Further, for thosecases where there is a large amount of unburned carbon in the fly ash,there is also the problem that the binding power of the fly ash isinsufficient and hence the quality of the artificial lightweight ribdecreases.

As a result, a flotation method for separating the unburned carbon hasbeen proposed, in which water is added to the fly ash for slurrying,kerosene is added as a collector to the slurry, the surface of theunburned carbon is modified by a high speed shearing mixer, thecollector is attached on the surface of the unburned carbon, and aflother is then added (for example, refer to Patent Document 1).

As shown in FIG. 7, the high speed shearing mixer (1) is composed of thehorizontal vessel (2), a number of toroidal partition walls (4) whichdivide the inside of the vessel (2) into various chambers (3), theaxially directed rotating shaft (5) which passes through the vessel (2)and the various stirring blades (6) which are fixed to the rotatingshaft (5) and rotate inside the various chambers (3). However, becauseof the shearing force applied on the slurry from the stirring blades (6)after the addition of the capturing agent, it is necessary to maintain ahighly precise clearance between the partition walls (4) and thestirring blades (6) or between the vessel (2) and the stirring blades(6). Furthermore, because of the length of the shaft, high technologyhas been required for the manufacture and maintenance of the high speedshearing mixer. In the diagram, (7) is the motor and (8) is thereduction gear.

Additionally, because in a conventional high speed shearing mixer therotary shaft (5) is horizontal in the vessel (2), an axial seal in thegap between the vessel (2) and the rotary shaft (5) has beenindispensable. Furthermore, when the vessel (2) has been scaled up froma horizontal type in a conventional high speed mixer, the distancebetween the slurry inlet and slurry outlet has been lengthened and ithas been difficult to freely change the fly ash generating conditionsand the processing time for surface modification or the processingconditions depending on, for example, the combustion temperature orcombustion method or type or composition of the coal.

Patent Document 1: Japanese Patent No. 3613347

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

This invention has been developed in order to resolve theabove-mentioned problems. Its objective is to provide an apparatus forremoving unburned carbon from fly ash that, even though its constructionis simple compared to a conventional high speed shearing mixer, caneffectively separate the unburned carbon by conforming to the nature ofthe fly ash wherein through surface modification a flotation method isapplied and the unburned carbon in the fly ash is removed.

Means for Solving the Problem

In order to resolve the above-mentioned problems, this invention has thestructure given below.

The device for removing unburned carbon from fly ash pertaining to claim1 is constructed of a slurry adjusting reservoir in which a slurry isgenerated with the addition of water to the fly ash, an added collectordevice for the addition of a collector in the above-mentioned slurry, avertical surface modification device that causes the collector to beattached on the surface of the unburned carbon in the slurry by means ofthe application of a shearing force through high speed stirring of theslurry after the addition of the collector, an adjusting reservoir inwhich a flother is added to the slurry whose surface has been modifiedby means of the above-mentioned surface modification device and aflotation unit in which the unburned carbon is floated and separatedalong with the air bubbles from the slurry after the addition of theflother.

The device for removing unburned carbon from fly ash of claim 1pertaining to claim 2 is characterized by having a structure thatconnects multiple surface modifying devices in series composed ofvertical type stirring units comprised of the above-mentioned surfacemodification device and stirring blades along with a vertical typestirring tank.

The device for removing unburned carbon from fly ash of claim 1pertaining to claim 3 is characterized by having a structure composed ofmultistage toroidal partitions with the above-mentioned surfacemodification device set up on the inner surface of the said stirringtank, a rotating shaft set up axially in the above-mentioned stirringtank and a vertical multistage stirring tank composed of stirring bladesset up alternately with the said partitions on the said rotating shaft.

The device for removing unburned carbon from fly ash described in anyone of claim 1 to 3 pertaining to claim 4 is characterized by applying ashearing force on the slurry after the addition of the collector andapplies a 10 to 100 kWh/m³ agitation force per unit slurry amount.

The device for removing unburned carbon from fly ash of claim 2 or 3pertaining to claim 5 is characterized by having a clearance of 2 to 100mm between the stirring tank and the stirring blades.

The device for removing unburned carbon from fly ash of claim 2pertaining to claim 6 is characterized by having a bypass channel thatin addition to connecting the adjacent vertical stirring tank through aconnecting tube goes around the stirring tank which is fixed to the saidconnecting tube.

EFFECTS OF THE INVENTION

From the above, because the invention pertaining to claim 1 isconstructed of a slurry adjusting tank in which a slurry is generatedwith the addition of water, a collector addition device in which acollector is added to the slurry, a vertical surface modification deviceon which the collector is attached on the surface of the unburned carbonin the slurry through high speed stirring of the slurry after thecollector is added and the application of a shearing force, an adjustingtank in which a flother has been added to the slurry which has beensurface modified by the surface modification device and a floatationunit in which the unburned carbon along with air bubbles is floated andseparated, an axial seal for the surface modification device that doeshigh speed stirring of the slurry and applies a shearing force after theaddition of the collector not only is unnecessary, but also possible toreduce the setup area of the surface modification device when comparedto a conventional horizontal type high speed shearing mixer. As aresult, it is possible to improve serviceability and operability atmaintenance time.

Because the invention pertaining to claim 2 has a structure in which theabove-mentioned surface modification device and a vertical stirring unithaving stirring blades are connected in series with a vertical stirringtank and a multistage shearing force is applied, despite being a simpledevice compared to a conventional horizontal type high speed shearingmixer, it is possible to modify the surface of the unburned carbonthrough conforming to the nature of the various types of fly ash inpulverized coal combustion boilers or fluidized bed combustion furnaces,that is, it is possible to effectively attach the collector on thesurface of the unburned carbon.

Furthermore, because the rotating shaft is horizontal to the vessel in aconventional horizontal high speed shearing mixer, a shaft seal in thespace between the vessel itself and the rotating shaft has beenindispensable but with the surface modification device of this inventionthe stirring tank is vertical so that a shaft seal for the stirring unitis unnecessary. As a result, it is possible to improve bothserviceability and operability at maintenance time. Furthermore, byvarying the number of stirring tanks used, it is possible to arbitrarilychange the generating conditions of the fly ash, that is, the processingtime or processing conditions depending on the combustion temperature orcombustion method or the type or structure of the coal. Additionally, byincreasing the number and size of the stirring tanks, with thisinvention it is possible to easily scale up the surface modificationdevice.

Because the invention pertaining to claim 3 has multistage toroidalpartitions with the above-mentioned surface modification device set upon the inner surface of the said stirring tank, a rotating shaft set upaxially in the above-mentioned stirring tank and a vertical multistagestirring tank composed of stirring blades set up alternately with thesaid partitions on the said rotating shaft, the seal of the rotatingshaft that does high speed stirring of the slurry and applies a shearingforce after the addition of the collector not only is just one-sided,compared to a conventional horizontal high speed shearing mixer it ispossible to reduce the setup area of the surface modification device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the device for removing unburned carbonfrom fly ash pertaining to this invention.

FIG. 2 is a general schematic diagram of the device for removingunburned carbon from fly ash pertaining to this invention.

FIG. 3 is an expanded plane diagram of the components of the surfacemodification unit.

FIG. 4 is an expanded side view diagram of the components of the surfacemodification unit.

FIG. 5 (a) is a state diagram when the collector is added. FIG. 5 (b) isa state diagram showing surface modification. FIG. 5 (c) is a statediagram when the flotation device is used.

FIG. 6 is a side view diagram that includes a partial cross-section ofthe vertical type multistage stirring unit pertaining to this invention.

FIG. 7 is a side view diagram that includes a partial cross-section of aconventional high speed shearing mixer.

DETAILED DESCRIPTION OF THE INVENTION

An explanation is given below for using the diagrams for configurationalrealization of this invention.

As shown in FIG. 1, the device for removing unburned carbon from fly ashpertaining to this invention is principally constructed of a slurryadjusting tank (10), a surface modification unit (30), an adjusting tank(60) and a flotation unit (70) for removing unburned carbon (b) from flyash. In the diagram, (c) is water, (e) is the collector, (f) is theflother and (a′) is the ash content.

As shown in FIG. 2, the slurry adjusting tank (10) is set up so that thewater (c) is mixed with the fly ash and the slurry (d) is generated. Thestirring blade (11) is provided to stir the slurry (d). Theconcentration of the fly ash is adjusted to be in the range of 5 to 40 wt % or 10 to 25 w t %.

The slurry adjusting tank (10) has a water providing device set up withthe fly ash tank that is not shown in the previous stage and it has apump (12) that supplies the slurry (d) to the surface modificationdevice (30). Subsequent to the pump (12) a collector tank (20) thataccommodates the collector (e), i.e., kerosene, light oil or heavy oil,a pump (21) which adds the collector (e) inside the collector tank (20)to the slurry (d) and a collector coupling tube (22) are provided. Thiscollector coupling tube (22) is connected to the slurry supply tube (13)which connects the surface modification device (30) to the slurryadjusting tank (10). The collector (e) is added to the slurry (d) insidethe slurry providing tube (13). The added amount of the collector shouldbe in the range of 0.01 to 3.0 w t % (fly ash ratio) or 0.05 to 1.0 w t% (fly ash ratio).

The surface modification device (30) is set up so a shearing force isapplied on the slurry with the collector and the surface of the unburnedcarbon is modified and is so constructed that the various surfacemodification units (31) are connected in series through the connectingtube (32). The surface modification unit (31) is variously constructedof a vertical stirring tank (33) and a vertical stirring unit (34) setup inside this stirring tank (33). The stirring unit (34) is constructedof a rotating shaft (35), a stirring blade (36) set up at the tip of theunit and a motor (37) which causes the stirring blade (36) to rotate athigh speed.

For the configuration of the stirring blade, it is preferable to haveits configuration be strip-like from a side view. Furthermore, as shownin FIG. 3, it is permissible to have the abrasion body (45) set up atthe tip of the stirring blade (36) and to abrade the surface of theunburned carbon between the abrasion body (45) and the inner wallsurface of the stirring tank (33). As shown in FIG. 3, the shape of theabrasive body (45) from a plane view may be convex but it may also betrapezoidal or triangular. Furthermore, it is preferable to have aconfiguration whereby the surface of the unburned carbon can be abradedbetween the abrasion body (45) and the inner wall surface of thestirring tank (33).

Additionally, it is preferable if the space (clearance) (L) between thetip of the stirring blade (36) and the inner wall surface of thestirring tank (33) be in the range of 2 to 100 mm or 5 to 50 mm. Whenthe clearance between the inner wall surface of the stirring blade (33)and the tip of the stirring blade (36) is less than 2 mm, a high degreeof precision in the manufacturing of the surface modification unit isdemanded which makes the manufacturing costs high. Furthermore, when theclearance between the inner wall surface of the stirring tank (33) andthe tip of the stirring blade (36) exceeds 100 mm, the effectiveness ofthe surface modification of the unburned carbon is reduced.

Furthermore, the stirring blade (36) should apply an agitation force(agitation power) of 10 to 100 kWh/m³ per unit slurry or preferably anagitation force of 30 to 50 kWh/m³. When the agitation power of thestirring blade (36) per unit slurry is less than 10 kWh/m³, it isdifficult to have surface modification of the unburned carbon. On theother hand, when the agitation power of the stirring blade (36) per unitslurry exceeds 100 kWh/m³, it is possible to modify the surface of theunburned carbon but the amount of electricity consumed increasesrapidly. Furthermore, because of the increased abrasion inside thestirring tank, it is uneconomical.

Additionally, the slurry retention time is set up to be 0.1 to 10minutes or preferably 0.5 to 5 minutes. When the slurry retention timeis less than 0.1 minutes, it is difficult to carry out surfacemodification of the unburned carbon. On the other hand, when the slurryretention time exceeds 10 minutes, surface modification of the unburnedcarbon does not progress any farther so that setup costs and runningcosts increase making it uneconomical.

The surface modification device (30) is constructed of a number (threein the diagram) of surface modification units (31) which are connectedin series by the connecting tube (32) which has pumps (38). Furthermore,the surface modification device (30) has a bypass channel (39) that goesaround the final (No. 3) surface modification unit (31) and the slurrymodified in previous stages, that is, in the No. 1 and No. 2 surfacemodification units (31 a) and (32 b), is able to bypass the No. 3surface modification unit (31 c). The inlet (40) to the bypass channel(39) is connected to the No. 2 connecting tube (32) and the outlet (41)of the bypass channel (39) is connected to the No. 3 connecting tube(32). The bypass channel has a bulb (42) and the No. 2 connecting tube(32) has a bulb (43) on the trailing side from the connection point ofthe bypass channel (39).

The adjusting tank (60) has the flother (f) added by means of the pump(51) from the flother tank (50) supplied to the slurry provided from thesurface modification unit (30) and the mixture is blended at low speed.A stirring blade (61) is located inside.

MIBC (methyl isobutyl carbinol) is used as the preferable foaming agent.The amount of the flother should be 20 to 5,000 ppm or preferably 100 to1,000 ppm. When the added amount of the flother is less than 20 ppm,there is insufficient foaming action. On the other hand, when the amountof the flother exceeds 5,000 ppm, the flother costs increase.Furthermore, the recovery rate of the fly ash is reduced andadditionally the surrounding area is contaminated from the excess airbubbles.

At the end section of the adjusting tank (60) a pump (62) is positionedto provide the slurry (d) to the floatation unit (70) after the additionof the flother. The floatation unit (70) causes the unburned carbonafter modification to adhere to the air bubbles and they rise to thesurface and the unburned carbon (froth) and the fly ash (tail) with theunburned carbon removed are separated. A well-known conventionalfloatation unit is used.

As shown in FIG. 6, it is possible to use a vertical multistage stirringtank (101) as the above-mentioned surface modification device (30). Thisvertical multistage stirring tank (101) is constructed of a verticalstirring tank (102), toroidal partitions (104) set up at numerous pointson the inner surface of the stirring tank (102), a rotating shaft (105)set up on the shaft center of the stirring tank (102) and stirringblades (106) set up alternately with the above-mentioned partitions(104) on the rotating shaft (105). Furthermore, in the diagram (109) isthe slurry inlet and (110) is the slurry discharge outlet. Additionally,the clearance between the stirring tank (102) and the stirring blades(106), the agitation force (agitation power) of the stirring blades(106) and the slurry retention time are the same as in the previousexamples.

Next, an explanation is given concerning the operation of the device forremoval of the unburned carbon.

For this invention, the number of the surface modification units is tobe determined in advance depending on the nature of the fly ash. Forexample, for relatively easy to surface modify fly ash (e.g. fly ashfrom bituminous coal), the number of surface modification units is asmall number (two in the diagram). For difficult surface modificationfly ash (e.g. fly ash from general coal), a larger number of surfacemodification units is used (three in the diagram. Furthermore, forconvenience of explanation, an explanation is given when the number ofsurface modification units used is two. In this case, the bulb (42) ofthe bypass channel (39) is open and the bulb (43) of the No. 2connecting tube (32) is closed.

In FIG. 2 the fly ash (a) is supplied to the slurry adjusting tank (10)and, is mixed with water (c) producing the slurry (d). At this time, theconcentration of the slurried fly ash is adjusted, for example, to 5 to40 w t %. The slurry (d) is supplied to the No. 1 surface modificationunit (31 a) by the pump (12) and while on its way the collector (e) in aprescribed amount (e.g. 0.01 to 3.0 w t. % (fly ash ratio)) is addedfrom the collector tank (20).

The slurry (d) and the collector (e) provided to the No. 1 surfacemodification unit (31 a) has a shearing force applied to it from thestirring blade (36) rotating at high speed (e.g. 200 to 10,000 rpm). Theslurry (d) and the collector (e) to which a shearing force is applied inthe No. 1 surface modification unit (31 a) are supplied to the No. 2surface modification unit (31 b) and again a shearing force is applied.In this manner, the shearing force applied to the slurry and thecollector modifies the surface of the unburned carbon and the flotationbuoyancy is improved. On this point an explanation is given whilereferencing FIGS. 5 (a) to 5 (c).

As shown in FIG. 5 (a), the fly ash (a) in the water (c), the unburnedcarbon (b) and the collector (e) are only in a mixed state. Because theamount of unburned carbon adhering to the air bubbles together with thecollector in this state even when supplied to the slurry flotation unitis extremely minimal, it is not possible to effectively remove theunburned carbon in the fly ash from flotation.

However, when doing surface modification by applying a shearing force onthe slurry and collector of FIG. 5 (a), energy of activation istransitionally produced on the surface of the various dispersedparticles of the unburned carbon (b), the fly ash (a) and the collector(e) in the slurry and the surfaces become very oleophilic. The variousparticle surfaces of the oleophilic unburned carbon (b) and thecollector (e) cohere and their mutual surface energies drop with theresult that, as shown in FIG. 5 (b), the collector (e) adheres to theunburned carbon (b).

Accordingly, when using a flotation device for flotation, as shown inFIG. 5 (c) it is possible to improve the flotation buoyancy of theunburned carbon (b) after the unburned carbon (b) adhering to thecollector (e) adheres to the air bubble (n) and floats to the surface.

The modified slurry (d′) which is expelled from the No. 2 surfacemodification unit (31 b) is supplied to the adjusting tank (60) throughthe bypass channel (39). In this adjusting tank (60) a flother (f) suchas MIBC (methyl isobutyl carbinol) is added in a prescribed amount (e.g.20 to 5,000 ppm). The slurry (d″) with the added flother (f) is suppliedto the flotation unit (70) where it is floated.

The froth (i) that includes the unburned carbon is separated into solidand liquid materials by a filter press not shown in the diagram and theunburned carbon (c) is recovered. The liquid portion dehydrated by thefilter press is supplied to the slurry adjusting tank (10) through apump (not shown in the diagram) and is again added to the fly ashy. Onthe other hand, the tailings (fly ash) from the flotation device (70)are separated into solid and liquid materials by the solid/liquidseparator (centrifugal dehydrator) which is not shown in the diagram andused in a cement mixture as a product with ash content.

INDUSTRIAL APPLICABILITY

This invention can be applied in a desirable manner when removingunburned carbon effectively from fly ash generated in coal burningthermal electric power plants and fluidized bed combustion furnaces.

1. An apparatus for removing unburned carbon from fly ash, comprising aslurry adjusting tank in which a slurry is generated with the additionof water to fly ash, a collector addition device in which a collector isadded to the above-mentioned slurry, a vertical surface modificationdevice in which the slurry with added collector is stirred at high speedand through the application of a shearing force and the collector isattached to the surface of the unburned carbon in the slurry, anadjusting tank in which a flother is added to the slurry having itssurface modified by the surface modification device, and a flotationunit in which the unburned carbon is floated and separated along withthe air bubbles from the slurry after the flother has been added.
 2. Anapparatus for removing unburned carbon from fly ash of claim 1characterized by having a structure in which a number of the surfacemodification devices composed of a vertical stirring tank and a stirringunit with stirring blades are connected in series and a multistageshearing force is applied.
 3. An apparatus for removing unburned carbonfrom fly ash of claim 1, characterized by having a structure of avertical multistage stirring tank consisting of a vertical stirringtank, toroidal partitions set up at multiple points on the inner surfaceof the stirring tank, a rotating shaft set up on the center axis of thestirring tank and stirring blades set up alternately with the partitionson the rotating shaft.
 4. An apparatus for removing unburned carbon fromfly ash described in any one of claims 1 to 3, characterized by applyingan agitation force of 10 to 100 kWh/m³ per unit amount of slurry when ashearing force is applied to the slurry after a collector has beenadded.
 5. An apparatus for removing unburned carbon from fly ash ofclaim 2 or 3, characterized by having 2 to 100 mm clearances between thestirring tank and the stirring blades.
 6. An apparatus for removingunburned carbon from fly ash of claim 2, characterized by beingconnected to an adjacent vertical stirring tank by a connecting tube andhaving a bypass channel set up that bypasses the stirring tank fixed onthe connecting tube.